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Glossary of MinSE


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R

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Rutherford backscattering spectrometry.   This method requires a very high energy (0.5-4.0 MeV) particle (H+, D+, 3He+,4He+) beam which is directed normal to the sample surface.   The ions collide elastically with the lattice atoms of the sample.   Many are back-scattered and subsequently collected by a detector which counts their number and measures their energy.   It is an important faeture of RBS that the energy of the back-scattered particles  can be used as a basis to calculate the depth and/or mass of the sample atoms that caused the scattering.   During RBS the amplified detector signal is collected over a period of time by a multi-channel analyser.   The "raw data" is subsequently displayed as yield (proportional to the total number of back-scattered particles) against channel number (proportional to energy).   These results are then quantified with well proven computer simulation programs (e.g., see J. C. B. Simpson and L. G. Earwaker, Vacuum, 1984, 34, 899), which through iterative calculation enables the derivation of depth concentration profiles.   RBS is particularly suited to determining concentrations of high atomic number elements dispersed in a low atomic number matrix.       The maximum useful detection depth (below the surface) is about ≈1 µm.   Also see NRA.

Hungary flag RBS

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Any atmosphere which reacts with a surface or that combines with other species to form a surface coating or diffusion zone.  For example, controlled reactive atmospheres form the basis of gaseous nitriding, gaseous carburising, reactive ion plating and reactive sputter deposition.

Hungary flag Reagens atmoszféra

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Any medium which reacts with a surface or that combines with other species to form a surface coating or diffusion zone.  Controlled reactive media form the basis of many techniques, especially  thermochemical diffusion and deposition methods.

Hungary flag Reagáló közeg

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Any sputtering method whereby multicomponent coatings, such as interstitial compounds, can be produced by sputtering into a reactive atmosphere, e.g., transition metals can be sputtered into nitrogen or carbonacous enriched atmospheres to produce, respectively,  transition metal nitrides (diagram) or carbides according to the following generalised equations (where M equates to the metal component):

2M + N2 --> 2MN

M + CH4 --> MC + 2H2

Reactive sputtering is deployed in both magnetron and non-magnetron sputtering modes of operation.   The former is preferred because of its higher deposition rate.   See magnetron sputtering.

Hungary flag reakcióképes katódporlasztás

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Residual elastic stress (actually strain) within a material; subdivided into macrostress and microstress.    Macrostress is residual elastic stress (strain) that occurs in a very large number of grains and is transmitted across adjacent grain boundaries.    Microstress is elastic stress (strain) confined to individual grains that is not transmitted across adjacent grain boundaries.    Both types of stress are best measured using x-ray diffraction methods.   Macrostress is determined from the peak shift observed when an object (sample) is rotated through j (the angle between the plane normal and the surface normal) while fixed in a specific diffraction condition (i.e.,  at a specific 2q value); a plot of sin2j versus  (dj-d0)/d0 is obtained, where d0 is the unstrained d-spacing and dj,the strained d-spacing at a surface angular rotation of j.  The slope of this plot is used to calculate the residual macrostress,  provided Young's modulus (E) and poissons ratio for the material under investigation is known.     Microstress is determined from a numerical analysis of the peak broadening observed at very high angles of 2q.    Other methods of quantifying residual stress also exist; these encompass ultrasound, neutron diffraction, microdrilling and magnetic field techniques.

Hungary flag Belső feszültség

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 Moderate quantities of retained austenite are unavoidable in carburised cases.  When retained austenite exceeds ≈ 50 vol% there is a marked reduction in case hardness and fatigue strength (rolling contact and rotation-bending).   The usual cause of excessive retained austenite is a too much case carbon (> 0.9wt-%) caused by a too high carbon potential.   Retained austenite is always most noticable at component corners, where, during carburising,  carbon is being supplied via two faces.  In the worst examples, massive, blocky iron carbides can from at the corners.   The quantification of retained austenite is best achieved by using an x-ray diffraction procedure.  Commonly the ratio of the intensities of the {200}a' to that of the {111}g are used for this purpose.

Hungary flag maradék ausztenit

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A method of hardening surfaces through localised cold working.  In the case of cylinderical objects, the surface is pressed between three rolls, which are rotated over the surface, while applying sufficient pressure to cause plastic deformation.  The cold worked surface remains in a state of residual compressive stress,  imparting a marked increase in fatigue strength.   This technique is applied to high strength steel, nickel and titanium alloy bolts.  High strength bolts, used for securing engine heads, are often strengthened below the bolt head using roll hardening; it is very effective in preventing dangerous fatigue failures.   For a practical review of this technology,  see: G. Turlach, Surf. Eng., 1985, 1, 17-22.

Hungary flag Felületkeményítés hengerléssel

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An effect that takes place by the conjoint action of rolling contact and traction stresses as typified in the operation of gears, i.e., where there is continous contact between two surface moving at slightly (≈10%) dissimilar surface speeds.    Nitriding and carburising are probably the two most important surface engineering methods that markedly improve the rolling contact fatigue endurance of steels.  The diagram (based on data from M. Weck and K. Schlotermann, Metallurgia, 1984, No 8,  328-332) shows the effectiveness of plasma nitriding in raising the fatigue strength and endurance of gear teeth made from prior hardened and tempered low alloy steels (designated DIN 31CrMoV9V and 16MnCr5N); note: the nitrided case depth is given in parentheses.    The plain carbon steel (DIN CK45), containing no nitride forming elements, has a fatigue strength and endurance only slightly better than an untreated steel;  hence, this material was in the nitrocarburised state and had an outer surface layer of e-carbide, several micrometers thick.  

Hungary flag Hengerlési kifáradás

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In the case of untreated steel surfaces, rolling contact fatigue stresses result in the formation of localised surface failures, which result in cavities ≈ 20 to 100 µm across, being formed.      For treated (carburised or nitrided) or untreated steels, superficial surface plastic deformation can also take place.   In the absence of an oil based lubricant, mild or severe oxidational wear also contributes to the overall wear.

Hungary flag kopás


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